Various forms of nucleic acid are used in a variety of fields. For example, in the field of recombinant nucleic acid technology, nucleic acid is used in the form of probe, genomic nucleic acid and plasmid nucleic acid.
In the field of diagnostics, nucleic acid is used in various forms for various purposes. For example, a nucleic acid probe is routinely used in the detection and diagnosis of a human pathogen. Likewise, it is used for the detection of genetic disorders. It is also used for the detection of a food contaminant. Moreover, it is routinely used in locating, identifying and isolating nucleic acid of interest for a variety of reasons ranging from genetic mapping to cloning and recombinant expression.
In recent years, a method for identification of RNA expression has been developed such as Real-time PCR or microarray, and the correlation between RNA expression pattern and disorder, drug efficacy or the like has been examined with great importance.
In most cases, nucleic acid can be obtained only in an extremely small amount, and its separation and purification operations are complex and require time. These time-consuming complex operations are apt to cause loss of nucleic acid. RNA is very unstable, and thus can be easily degraded by heat, alkali and especially RNase. Therefore, it is very difficult to separate and purify highly pure RNA without having it degraded.
In purifying nucleic acid from samples obtained from serum, urine and bacterial cultures, there is an additional risk of contamination and false-positive result.
One of the well-known separation and purification methods comprises adsorption of nucleic acid on a solid phase such as silicon dioxide, silica polymer or magnesium silicate, and subsequent step such as washing or desorption (e.g., JP-B No. 7-51065 Patent Document 1). However, these methods involve problems of being not sufficient in simplicity, swiftness, and suitability for automation and reducing tool or apparatus size used in these methods, although high in isolation performance. The other problems come from the tools, apparatus and particularly adsorbents, including difficulty in production of an adsorbent of identical performance on an industrial scale, handling and realizing various shapes. Further, due to the fragility of a material and requiring a certain thickness or more to obtain mechanical strength, especially, in order to homogeneously interact DNase on a solid phase when degrading DNA with DNase for selectively recovering RNA from a mixture sample containing DNA and RNA, there are drawbacks such as requiring the DNase solution in a certain amount or more. DNase is relatively expensive, so that this could become a problem in case of selectively recovering RNA which necessity is predicted to increase much more in the future.
Further, one of the methods for separating and purifying nucleic acid simply and effectively is to use a solution for adsorbing nucleic acid onto a solid phase and a solution for desorbing nucleic acid from the solid phase membrane so that there is provided a method for separating and purifying nucleic acid by adsorbing and desorbing onto and from the solid phase comprising an organic polymer having a hydroxyl group on a surface thereof (JP-A No. 2003-128691 Patent Document 2). This method, however, needs further improvement.
Examples of other related known methods for separating and purifying nucleic acid include methods using centrifuge, magnetic beads and a filter. Further, an apparatus for separating and purifying nucleic acid, which use these methods, have been proposed. For example, an apparatus for separating and purifying nucleic acid using filter, wherein several filter tubes receiving filters are set on a rack, and therein a sample solution containing nucleic acid is injected where the bottom portion of the rack is applied with a sealing agent and sealed with an air chamber to reduce an inner pressure. Simultaneously the sample solution containing nucleic acid is sucked from the discharging side and passed through all filter tube, so as to adsorb nucleic acid onto the filter. Afterwards, a washing solution and a recovering solution are injected and again sucked thereto under reduced pressure so that washing and desorbing are also carried out. An automated apparatus using these procedures has been proposed. (e.g., Japanese Patent No. 2832586 Patent Document 3).
[Patent Document 1] JP-B No. 7-51065
[Patent Document 2] JP-A No. 2003-128691
[Patent Document 3] Japanese Patent No. 2832586